This invention relates to a photothermographic material. More specifically, it relates to a photothermographic material wherein a specific fluorine compound is employed so as to lessen changes in photographic properties of the photothermographic material in the storage state and under environmental conditions in using.
In recent years, it has been strongly required in the field of medicine to reduce the volume of liquid wastes from the viewpoints of environmental protection and space saving. Accordingly, there have been needed techniques concerning photosensitive thermographic materials for medical diagnosis and photographic uses which can be efficiently exposed with a laser image setter or a laser imager so as to give vivid black images having a high resolution and an excellent sharpness. Use of these photosensitive thermographic materials makes it possible to supply to clients a more convenient thermal development system which is nondetrimental to the environment since no chemical is needed for solvent treatments.
Although there arises the same demand in the filed of general image forming materials, high image qualities with an excellent sharpness and graininess are necessary in medical images which should be finely formed. Moreover, there is an additional feature that images in a cool black tone are preferred from the viewpoint of convenience in diagnosing. Although various hard copy systems with the use of pigments and dyes such as ink jet printers and electrophotographs are commonly employed today as image forming systems, there is no output system satisfactory for medical images.
On the other hand, there have been reported thermal image forming systems using organic silver salts, for example, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d described in U.S. Pat. Nos. 3,152,904 and 3,457,075 and B. Shely (Image Processes and Materials) Neblette, 8th ed., Sturge, V. Walcorth, ed. by A. Shepp, p.2 (1996). In particular, a photothermographic material generally has a photosensitive layer wherein a catalytically active amount of a photocatalyst (for example, a silver halide), a reducing agent and a reducible silver salt (for example, an organic silver salt) together with, if needed, a color tone controller which controls the silver color tone are dispersed in a binder matrix. After exposure, the photothermographic material is heated to a high temperature (for example, 80xc2x0 C. or above). Thus, the silver halide or the reducible silver salt (serving as an oxidizing agent) and the reducing agent undergo a redox reaction to thereby form a silver image in a black color. The redox reaction is accelerated by the catalytic action of the latent image of the silver halide formed by the exposure. Therefore, the silver image in the black color is formed in the exposed region. Fuji Medical Dry Imager FM-DP L has been disclosed in a number of documents including U.S. Pat. No. 2,910,377 and JP-B-43-4924 and put into the market as a medical image forming system with the use of a photothermographic material.
To produce a thermal image forming system with the use of an organic silver halide, use is made of a production method wherein a coating solution containing a solution of a main binder polymer dissolved in an organic solvent is applied and dried, or another production method wherein an aqueous coating solution containing an aqueous dispersion of fine grains of a main binder polymer is applied and dried. Since no solvent recovery step is needed in the latter method, it can be carried out by using a simple production apparatus and is advantageous in mass production.
Owing to the characteristics as described above, photothermographic materials have gained popularity in the market. Thus, they have been employed in expanding fields and sites. With this tendency, it has been required to further improve the performance thereof. Among all, it is frequently required to improve the finishing stability and, therefore, attempts have been vigorously made to improve the storage properties and using environment-dependency of photothermographic materials.
An object of the invention is to lessen changes in photographic performance of a photothermographic material in the storage state. Another object thereof is to lessen changes in photographic performance caused by the environmental temperature and humidity in using a photothermographic material. Thus, it is intended to provide a photothermographic material showing lessened changes in the photographic performance as described above.
The objects of the invention have been achieved by the following photothermographic materials.
(1) A photothermographic material containing, on one side of a substrate, at least one photosensitive silver halide, non-photosensitive organic silver salts, a reducing agent for thermal development and a binder, characterized by containing a fluorine compound having one or more fluoroalkyl groups carrying 2 or more carbon atoms and not more than 13 fluorine atoms and at least one of anionic and nonionic hydrophilic groups, and silver behenate amounting to 40 to 98% by mol of the non-photosensitive organic silver salts.
(2) A photothermographic material as described in the above (1) characterized in that the fluorine compound is a compound represented by the following formula (F).
Formula (F): 
wherein R1 and R2 represent each a substituted or unsubstituted alkyl group and at least one of them represents a fluoroalkyl group carrying 2 or more carbon atoms and not more than 13 fluorine atoms; R3 and R4 represent each a hydrogen atom or an alkyl group; and A represents xe2x80x94Lbxe2x80x94SO3xe2x80x94M (wherein M represents a hydrogen atom or a cation; and Lb represents a single bond or a substituted or unsubstituted alkylene group.
(3) A photothermographic material as described in the above (2) characterized in that, in the compound represented by the formula (F), R3 and R4 are both hydrogen atoms.
(4) A photothermographic material as described in the above (2) or (3) characterized in that, in the compound represented by the formula (F), Lb is a xe2x80x94CH2xe2x80x94 group.
(5) A photothermographic material as described in any of the above (2) to (4) characterized in that, in the compound represented by the formula (F), at least one of R1 and R2 is a fluoroalkyl group carrying 4 or more carbon atoms and not more than 11 fluorine atoms.
(6) A photothermographic material as described in any of the above (2) to (4) characterized in that, in the compound represented by the formula (F), R1 and R2 are each a fluoroalkyl group carrying 4 or more carbon atoms and not more than 11 fluorine atoms.
(7) A photothermographic material as described in any of the above (1) to (6) characterized in that silver behenate amounts to 50 to 85% by mol of the non-photosensitive organic silver salts.
(8) A photothermographic material as described in any of the above (1) to (7) characterized in that the total coating dose of silver is 1.9 g/m2 or less.
(9) A photothermographic material as described in the above (8) characterized in that the total coating dose of silver is 1.6 g/m2 or less.
(10) A photothermographic material as described in any of the above (1) to (9) characterized in that the reducing agent for thermal development is represented by the following formula (R): 
wherein R11 and R11xe2x80x2 independently represent each an alkyl group having 1 to 20 carbon atoms; R 12 and R12xe2x80x2 independently represent each a hydrogen atom or a substituent capable of attaching to a benzene ring; L represents a xe2x80x94Sxe2x80x94 group or a xe2x80x94CHR13xe2x80x94 group (wherein R13 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms); and X1 and X1xe2x80x2 independently represent each a hydrogen atom or a group capable of attaching to a benzene ring as a substituent.
(11) A photothermographic material as described in any of the above (1) to (10) characterized by containing a compound represented by the formula (D) in the same side of the substrate as the image forming layer: 
wherein R21 to R23 independently represent each an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an amino group or a heterocyclic group which may be either unsubstituted or substituted.
(12) A photothermographic material as described in any of the above (1) to (11) characterized by containing a compound represented by the formula (H) in the same side of the substrate as the image forming layer:
Qxe2x80x94(Y)nxe2x80x94C(Z1)(Z2)Xxe2x80x83xe2x80x83(H)
wherein Q represents an alkyl group, an aryl group or a heterocyclic group; Y represents a divalent linking group; n is 0 or 1; Z1 and Z2 represent each a halogen atom; and X represents a hydrogen atom or an electron-withdrawing group.
(13) A photothermographic material as described in any of the above (1) to (12) characterized by containing a development accelerator having an effect of accelerating thermal development on the reducing agent for thermal development represented by the formula (R).
(14) A photothermographic material as described in the above (13) characterized in that the development accelerator is a hydrazine compound.
(15) A photothermographic material characterized in that the compound represented by the formula (F) is contained in the undercoating layer of the substrate.
(16) A photothermographic material as described in any of the above (1) to (14) characterized in that the compound represented by the formula (F) is contained in the undercoating layer of the substrate.